electrical power systems technology third edition pdf

15 The System Concept—Basic System Functions—A Simple Electrical System Example—Energy, Work, and Power—Types of Electrical Circuits—Power in DC Electrical Circuits— Maximum Power Trans

Electrical Power Systems Technology / Stephen W Fardo, Dale R Patrick

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Units of Measurement—Conversion of SI Units—

Scientific Notation

Chapter 2 Power System Fundamentals 15

The System Concept—Basic System Functions—A Simple Electrical System Example—Energy, Work, and Power—Types

of Electrical Circuits—Power in DC Electrical Circuits—

Maximum Power Transfer—Overview of Alternating Current (AC) Circuits—Vector and Phasor Diagrams—Impedance in

AC Circuits—Power Relationships in AC Circuits—Power Relationships in Three—Phase Circuits

Chapter 3 Power Measurement Equipment 59

Measurement Systems—Measuring Electrical Power—

Measuring Electrical Energy—Measuring Three-Phase Electrical Energy—Frequency Measurement—Synchroscopes—

Ground -Fault Indicators—Megohmeters—Clamp-On Meters Telemetering Systems

UNIT II ELECTRICAL POWER PRODUCTION SYSTEMS 79Chapter 4 Modern Power Systems 83

Electrical Power Plants—Fossil Fuel Systems—Steam Turbines— Boilers—Hydroelectric Systems—Nuclear Fission Systems— Operational Aspects of Modem Power Systems

Chapter 5 Alternative Power Systems 117

Potential Power Sources—Solar Energy Systems—Geothermal Power Systems—Wind Systems—Magnetohydrodynamic (MHD) Systems—Nuclear-Fusion Power Systems—Nuclear-Fusion Methods—Future of Nuclear Fusion—Fuel-Cell Systems—Tidal Power Systems—Coal-Gasification Fuel Systems—Oil-Shale Fuel-Production Systems—Alternative Nuclear Power Plants— Biomass Systems

Single-Phase AC Power Systems—Single-Phase AC Generators— Three-Phase AC Generators—High-Speed and Low-Speed Generators—Generator Frequency—Generator Voltage

Regulation—Generator Efficiency

Chapter 7 Direct Current Power Systems 157

DC Production Using Chemical Cells—Characteristics of Primary Cells—Characteristics of Secondary Cells—DC Generating Sys- tems—DC Conversion Systems—DC Filtering Methods—DC Reg- ulation Methods

UNIT III ELECTRICAL POWER DISTRIBUTION SYSTEMS 203Chapter 8 Power Distribution Fundamentals 207

Overview of Electrical Power Distribution—Power Transmission and Distribution—Radial, Ring, and Network Distribution Systems—Use of Transformers for Power Distribution—

Conductors in Power Distribution Systems—Conductor Area— Resistance of Conductors—Conductor Sizes and Types—

Ampacity of Conductors—Ampacity Tables—Use of Insulation in Power Distribution Systems

Chapter 9 Power Distribution Equipment 239

Equipment Used at Substations—Power System Protective Equipment—Power Distribution Inside Industrial and

Commercial Buildings—The Electrical Service Entrance—Service Entrance Terminology

Chapter 10 Single-Phase and Three-Phase

Distribution Systems 255Single-Phase Systems— Three-Phase Systems—Grounding

of Distribution Systems—System Grounding—Ground-Fault Protection—Wiring Design Considerations for Distribution Systems—Branch Circuit Design Considerations—Feeder Circuit Design Considerations—Determining Grounding Conductor Size—Parts of Interior Electrical Wiring Systems

UNIT IV ELECTRICAL POWER CONVERSION SYSTEMS 289Chapter 11 Fundamentals of Electrical Loads 293

Load Characteristics—Three-Phase Load Characteristics

Chapter 12 Heating Systems 307

Basic Heating Loads—Electrical Welding Loads—Power Considerations for Electric Welders—Electric Heating and Air Conditioning Systems Chapter 13 Lighting Systems 327

Characteristics of Light—Electrical Lighting Circuits— Branch Circuit Design—Lighting Fixture Design— Factors in Determining Light Output Chapter 14 Mechanical Systems 349

Basic Motor Principles—DC Motors—Specialized DC Motors— Single-Phase AC Motors—Three-Phase AC Motors—Specialized Mechanical Power Systems—Electric Motor Applications UNIT V ELECTRICAL POWER CONTROL SYSTEMS 401

Chapter 15 Power Control Devices 405

Power Control Standards, Symbols, and Definitions—Power Control Using Switches—Control Equipment for Electric Motors—other Electromechanical Power Control Equipment— Electronic Power Control Chapter 16 Operational Power Control Systems 427

Basic Control Systems—Motor—Starting Systems— Specialized Control Systems—Frequency—Conversion Systems—Programming the PLC Chapter 17 Control Devices 453

Silicon Controlled Rectifiers—SCR Construction—SCR I-V Characteristics—DC Power Control with SCRs—AC Power Control with SCRs—Triac Power Control—Triac Construction— Triac Operation—Triac I-V Characteristics—Triac Applications— Static Switching—Start-Stop Triac Control—Triac Variable Power Control—Diac Power Control—Electronic Control Considerations Appendix A Trigonometric Functions 471

Appendix B The Elements 473

Appendix C Metric Conversions 475

Index 481

Preface

Electrical Power Systems Technology (Third Edition) provides a broad

overview of the production, distribution, control, conversion, and surement of electrical power The presentation method used in this book will allow the reader to develop an understanding of electrical power sys-tems The units of the book are organized in a systematic manner, begin-ning with electrical power production methods The fundamentals of each major unit of the book are discussed at the beginning of the unit These fundamentals provide a framework for the information that follows in each unit The last unit has been expanded to include control devices.This book deals with many important aspects of electrical power, not just with one or two areas In this way, it will give the reader a better un-

mea-derstanding of the total electrical power system—from the production of

electricity to its conversion to other forms of energy Each unit deals with

a specific system, such as production, distribution, control, conversion, or measurement Each system is broken down into subsystems The subsys-tems are then explored in greater detail in the chapters that make up each unit

In order to understand the contents of this book in depth, the reader should have a knowledge of basic electrical fundamentals The mathemat-ical presentations given are very simple and are used only to show the practical relationships that are important in electrical power system op-eration This book is recommended as a textbook for an “electrical power”

or “electrical generators and motors” course It would be a suitable text for vocational-technical schools, community colleges, universities, and, pos-sibly, some technical high school programs Many illustrations are shown,

to make the presentations that are given easier to understand The content

is presented in such a way that any reader should be able to learn a great deal about the operation of electrical power systems

Stephen W Fardo Dale R Patrick Eastern Kentucky University Richmond, KY 40475

UNIT I

Power Measurement Systems

and Fundamentals

In order to understand electrical power measurement systems, we must

first study the fundamentals of measurement These fundamentals deal mainly with the characteristics and types of measurement systems Mea-surement systems are discussed in Chapter 1

Chapter 2 provides an overview of the fundamentals that are

impor-tant in the study of electrical power systems

Chapter 3 deals with measurement equipment and methods associated

with electrical power systems These measurement systems include gle-phase and three-phase wattmeters, power factor meters, ground-fault indicators, and many other types of equipment used in the analysis of electrical power system operation

sin-Figure I shows a block diagram of the electrical power systems model

used in this textbook This model is used to divide electrical power

sys-tems into five important syssys-tems: (1) Power Measurement, (2) Power tion, (3) Power Distribution, (4) Power Conversion, and (5) Power Control.

Produc-UNIT OBJECTIVES

Upon completion of Unit I, Power Measurement Systems and damentals, you should be able to:

Fun-Power Measurement Fundamentals (Chapter 1)

Power System Fundamentals (Chapter 2)

Power Measurement Equipment (Chapter 3)

Figure I Electrical power systems model

1

1 Compare the basic systems used for measurement.

2 Convert quantities from small units to large units of

measurement

3 Convert quantities from large units to small units of

measurement

4 Convert quantities from English to metric units

5 Convert quantities from metric to English units

6 Explain the parts of an electrical system

7 Calculate power using the proper power formulas

8 Draw diagrams illustrating the phase relationship between current and voltage in a capacitive circuit or inductive circuit

9 Define capacitive reactance and inductive reactance

10 Solve problems using the capacitive reactance formula and inductive reactance formula

11 Define impedance

12 Calculate impedance of series and parallel AC circuits

13 Determine current in AC circuits

14 Explain the relationship between AC voltages and current in resistive circuits

15 Describe the effect of capacitors and inductors in series and in parallel

16 Explain the characteristics of series and parallel AC circuits

17 Solve Ohm’s law problems for AC circuits

18 Solve problems involving true power, apparent power, power factor, and reactive power in AC circuits

19 Explain the difference between AC and DC

20 Define the process of electromagnetic induction

21 Describe factors affecting induced voltage

22 Draw a simple AC generator and explain AC voltage generation

23 Convert peak, peak-peak, average, and RMS/effective values from one to the other

24 Describe voltage, current, and power relationships in three-phase

AC circuits for wye and delta configurations

25 Describe the following basic types of measurement systems: Analog Instruments

Comparative Instruments

CRT Display Instruments

Numerical Readout Instruments

Chart Recording Instruments

26 Explain the operation of an analog meter movement.

27 Describe the function of a Wheatstone bridge

28 Explain the use of the dynamometer movement of a wattmeter to measure electrical power

29 Describe the use of a watt-hour meter to measure electrical energy

30 Interpret numerical readings taken by a watt-hour meter

31 Explain the use of a power analyzer to monitor three-phase power

32 Describe the measurement of power factor with a power factor meter

33 Calculate power demand

34 Explain the monitoring of power demand

35 Explain the methods of measuring frequency

36 Explain the use of a synchroscope

37 Describe the use of a ground fault indicator

38 Describe the use of a megohmmeter to measure high resistance values

39 Describe the operation of a clamp-on current meter

40 Describe a telemetering system

Today, most nations of the world use the metric system of ment In the United States, the National Bureau of Standards began a study

measure-in 1968 to determmeasure-ine the feasibility and costs of convertmeasure-ing the nation to the metric measurement system Today, this conversion is incomplete.The units of the metric system are decimal measures based on the kilogram and the meter Although the metric system is very simple, several countries have been slow to adopt it The United States has been one of these reluctant countries, because of the complexity of actions required by a complete changeover of measurement systems

IMPORTANT TERMS

Chapter 1 deals with power measurement fundamentals After studying this chapter, you should have an understanding of the following terms:

Units of Measurement

Measurement Standards

English System of Units

International System of Units (SI)

Unit Conversion Tables

Base Units

5

Derived Units

Small Unit Prefixes

Large Unit Prefixes

Units of measurement have a significant effect on our lives, but we

of-ten take them for granted Almost everything we deal with daily is sured by using some unit of measurement For example, such units allow

mea-us to measure the distance traveled in an automobile, the time of day, and the amount of food we eat during a meal Units of measurement have been in existence for many years; however, they are now more precise-

ly defined than they were centuries ago Most units of measurement are based on the laws of physical science For example, distance is measured

in reference to the speed of light, and time is measured according to the duration of certain atomic vibrations

The standards we use for measurement have an important effect on

modern technology Units of measurement must be recognized by all countries of the world There must be ways to compare common units of measurement among different countries Standard units of length, mass, and time are critical to international marketing and to business, industry, and science in general

The English system of units, which uses such units as the inch, foot,

and pound, has been used in the United States for many years However, many other countries use the metric system, which has units such as kilo-

meters, centimeters, and grams The metric system is also called the national System of Units, and is abbreviated SI Although the English and SI

Inter-systems of measurement have direct numerical relationships, it is difficult for individuals to change from one to the other People form habits of us-ing either the English or the SI system

Since both systems of measurement are used, this chapter will miliarize you with both systems, and with the conversion of units from

fa-one to the other The conversion tables of Appendix C should be helpful

The SI system, which was introduced in 1960, has several advantages over

Power Measurement Fundamentals 7

the English system of measurement It is a decimal system that uses units commonly used in business and industry, such as volts, watts, and grams The SI system can also be universally used with ease However, the use of other units is sometimes more convenient

The SI system of units is based on seven units, which are shown in

Table 1-1 Other units are derived from the base units and are shown in Table 1-2

Table 1-1 Base Units of the SE System

Luminous Intensity candela cd

Amount of substance mole mol

Electric conductance siemen S

————————————————————————

Some definitions of base units are included below:

1 Unit of length: METER (m)—the length of the path that light travels

in a vacuum during the time of 1/29,792,458 second (the speed of light)

2 Unit of mass: KILOGRAM (kg)—the mass of the international type, which is a cylinder of platinum-iridium alloy material stored in

proto-a vproto-ault proto-at Sevres, Frproto-ance, proto-and preserved by the Internproto-ationproto-al Bureproto-au

of Weights and Measures

3 Unit of time: SECOND (s)—the duration of 9,192,631,770 periods of radiation corresponding to the transition between two levels of a Cesium-133 atom (This is extremely stable and accurate.)

4 Unit of electric current: AMPERE (A)—the current that, if maintained

in two straight parallel conductors of infinite length, placed 1 meter apart in a vacuum, will produce a force of 2 × 10–7 newtons per meter between the two conductors

5 Unit of temperature: KELVIN (K)—an amount of 1/273.16 of the temperature of the triple point of water (This is where ice begins to form, and ice, water, and water vapor exist at the same time.) Thus,

0 degrees Centigrade = 273.16 Kelvins

6 Unit of luminous intensity: CANDELA (cd)—the intensity of a source that produces radiation of a frequency of 540 × 1012 Hertz

7 Unit of amount of substance: MOLE (mol)—an amount that contains

as many atoms, molecules, or other specified particles as there are atoms in 0.012 kilograms of Carbon-12

As you can see, these are highly precise units of measurement The definitions are included to illustrate that point Below, a few examples of

derived units are also listed:

1 Unit of energy: JOULE (J)—the work done when one newton is applied at a point and displaced a distance of one meter in the direction of the force; 1 joule = 1 newton meter

2 Unit of power: WATT (W)—the amount of power that causes the production of energy at a rate of 1 joule per second; 1 watt = 1 joule per second

3 Unit of capacitance: FARAD (F)—the capacitance of a capacitor in which a difference of potential of 1 volt appears between its plates when it is charged to 1 coulomb; 1 farad = 1 coulomb per volt

Power Measurement Fundamentals 9

4 Unit of electrical charge: COULOMB (C)—the amount of electrical charge transferred in 1 second by a current of 1 ampere; 1 coulomb =

1 ampere per second

CONVERSION OF SI UNITS

Sometimes it is necessary to make conversions of SI units, so that very large or very small numerals may be avoided For this reason, deci-

mal multiples and submultiples of the base units have been developed, by

using standard prefixes These standard prefixes are shown in Table 1-3 Multiples and submultiples of SI units are produced by adding prefixes to the base unit Simply multiply the value of the unit by the factors listed in Table 1-3 For example:

Small Units

The measurement of a value is often less than a whole unit, for

ex-ample 0.6 V 0.025 A, and 0.0550 W Some of the prefixes used in such

mea-surements are shown in Table 1-4

For example, a millivolt (mV) is 0.001 V, and a microampere (μA) is 0.000001 A The prefixes of Table 1-4 may be used with any electrical unit

of measurement The unit is divided by the fractional part of the unit For example, to change 0.6 V to millivolts, divide by the fractional part indi-cated by the prefix Thus, 0.6 V equals 600 mV, or 0.6 V ÷ 0.001 = 600 mV

To change 0.0005 A to microamperes, divide by 0.000001 Thus, 0.0005 A =

500 μA When changing a base electrical unit to a unit with a prefix, move the decimal point of the unit to the right by the same number of places in the fractional prefix To change 0.8 V to millivolts, the decimal point of 0.8 V is moved three places to the right (8.↵0↵0), since the prefix milli has three decimal places So 0.8 V equals 800 mV A similar method is used for converting any electrical unit to a unit with a smaller prefix

Table 1-4 Prefixes of Units Smaller Than 1

——————————————————————————————

Prefix Abbreviation Fractional Part of a Whole Unit

——————————————————————————————milli m 1/1000 or 0.001

(3 decimal places) micro μ 1/1,000,000 or 0.000001

(6 decimal places) nano n n 1/1,000,000,000 or 0.000000001

(9 decimal places) pico p 1/1,000,000,000,000 or 0.000000000001

(12 decimal places)

——————————————————————————————

When a unit with a prefix is converted back to a base unit, the prefix

must be multiplied by the fractional value of the prefix For example, 68

mV is equal to 0.068 V When 68 mV is multiplied by the fractional value

of the prefix (0.01 for the prefix milli), this gives 68 mV × 0.001 = 0.0068 V That is, to change a unit with a prefix into a base electrical unit, move the decimal in the prefix unit to the left by the same number of places as the value of the prefix To change 225 mV to volts, move the decimal point in

225 three places to the left ( 2 2 5 ), since the value of the prefix milli has three decimal places Thus, 225 mV equals 0.225 V.) ) )

Power Measurement Fundamentals 11

Table 1-5 Prefixes of Large Units

Sometimes electrical measurements are very large, such as 20,000,000

W, 50,000, or 38,000 V When this occurs, prefixes are used to make these numbers more manageable Some prefixes used for large electrical values are shown in Table 1-5 To change a large value to a smaller unit, divide the large value by the value of the prefix For example, 48,000,000 Ω is changed to 48 megohms (MΩ) by dividing by one million: 48,000,000 Ω

÷ 1,000,000 48 MΩ To convert 7000 V to 7 kilovolts (kV), divide by one thousand: 7000 V ÷ 1000 = 7kv To change a large value to a unit with a prefix, move the decimal point in the large value to the left by the number

of zeros represented by the prefix Thus 3600 V equals 3.6 kV ( 3 6 0 0 )

To convert a unit with a prefix back to a standard unit, the decimal point

is moved to the right by the same number of places in the unit, or, the number may be multiplied by the value of the prefix To convert 90 MΩ to ohms, the decimal point is moved six places to the right (90,000,000) The

90 MΩ value may also be multiplied by the value of the prefix, which is 1,000,000 Thus 90 MΩ × 1,000,000 = 90,000,000 Ω

The simple conversion scale shown in Figure 1-1 is useful when

con-verting standard units to units of measurement with prefixes This scale uses either powers of 10 or decimals to express the units

SCIENTIFIC NOTATION

Using scientific notation greatly simplifies arithmetic operations Any

number written as a multiple of a power of 10 and a number between 1 and 10 is said to be expressed in scientific notation For example:

81,000,000 = 8.1 × 10,000,000, or 8.1 × 107500,000,000 = 5 × 100,000,000, or 5 × 1080.0000000004 = 4 × 0.0000000001, or 4 × 10–10

) ) ) )

Power Measurement Fundamentals 13

Table 1-6 lists some of the powers of 10 In a whole-number power of

10, the power to which 10 is raised is positive and equals the number of

zeros following the 1 In decimals, the power of 10 is negative and equals the number of places the decimal point is moved to the left of the 1

Scientific notation simplifies multiplying and dividing large numbers or

small decimals For example:

Other Electrical Power Units

Table 1-7 shows some common units used in the study of electrical power systems These units will be introduced as they are utilized You should review this figure and the sample problems included in Appen-dix A

Table 1-7 Common Units

————————————————————————————————

————————————————————————————————

Speed of rotation radian per second (1 rad/sec = 9.55 r/min) rad/s

Temperature difference kelvin or degree Celsius K or °C

————————————————————————————————

Chapter 2

Power

System Fundamentals

One of the most important areas of electrical knowledge is the study

of electrical power Complex systems supply the vast need of our country for electrical power Because of our tremendous power requirement, we must constantly be concerned with the efficient operation of our power production and power conversion systems This textbook deals with the characteristics of electrical power production systems, power distribution systems, power conversion systems, and power control systems In addi-tion, an overview of electrical power measurement systems is included in this unit

Electrical Power Systems Model

Electrical Power Measurement

Electrical Power Production

Electrical Power Distribution

15

Electrical Power Conversion

Electrical Power Control

Maximum Power Transfer

Purely Resistive AC Circuit

Counter-Electromotive Force (CEMF)

Power System Fundamentals 17

Reactive Power (VARs)

Power per Phase (PP)

Total Three-Phase Power (PT)

THE SYSTEM CONCEPT

For a number of years, people have worked with jigsaw puzzles as a source of recreation A jigsaw puzzle contains a number of discrete parts that must be placed together properly to produce a picture Each part then plays a specific role in the finished product When a puzzle is first started,

it is difficult to imagine the finished product without seeing a tive picture

representa-Understanding a complex field such as electrical power poses a problem that is somewhat similar to the jigsaw puzzle, if it is studied by its discrete parts In this case, too, it is difficult to determine the role that a discrete part plays in the operation of a complex system A picture of the whole system, divided into its essential parts, therefore becomes an ex-tremely important aid in understanding its operation

The system concept will serve as the “big picture” in the study of

elec-trical power In this approach, a system will first be divided into a number

of essential blocks This will clarify the role played by each block in the eration of the overall system After the location of each block has been es-tablished, the discrete component operation related to each block becomes more relevant Through this approach, the way in which some of the “piec-es” of electronic systems fit together should be made more apparent.BASIC SYSTEM FUNCTIONS

op-The word system is commonly defined as an organization of parts

that are connected together to form a complete unit A wide variety of

electrical systems is in use today Each system has a number of unique features, or characteristics, that distinguish it from other systems More importantly, however, there is a common set of parts found in each sys-tem These parts play the same basic role in all systems The terms energy

source, transmission path, control, load, and indicator are used to describe

the various system parts A block diagram of these basic parts of the tem is shown in Figure 2-1

sys-Each block of a basic system has a specific role to play in the all operation of the system This role becomes extremely important when a detailed analysis of the system is to take place Hundreds and even thou-sands of discrete components are sometimes needed to achieve a specific block function Regardless of the complexity of the system, each block must achieve its function in order for the system to be operational Being familiar with these functions and being able to locate them within a complete system

over-is a big step toward understanding the operation of the system

The energy source of a system converts energy of one form into

some-thing more useful Heat, light, sound, and chemical, nuclear, and

mechan-Figure 2-1 Electrical system: (A) Block diagram; (B) Pictorial diagram

Power System Fundamentals 19

ical energy are considered as primary sources of energy A primary energy source usually goes through an energy change before it can be used in an operating system

The transmission path of a system is somewhat simpler than other

system functions This part of the system simply provides a path for the transfer of energy (see Figure 2-2) It starts with the energy source and continues through the system to the load In some cases, this path may

be a single electrical conductor, light beam, or other medium between the source and the load In other systems, there may be a supply line between the source and the load In still other systems, there may be a supply line between the source and the load, and also a return line from the load to the source There may also be a number of alternate or auxiliary paths within

a complete system These paths may be series connected to a number of small load devices, or parallel connected to many independent devices

The control section of a system is by far the most complex part of the

entire system In its simplest form, control is achieved when a system is turned on or off Control of this type can take place anywhere between the source and the load device The term “full control” is commonly used to describe this operation In addition to this type of control, a system may also employ some type of partial control Partial control usually causes some type of an operational change in the system, other than an on or off condition Changes in electric current or light intensity are examples of al-terations achieved by partial control

The load of a system refers to a specific part, or a number of parts,

de-signed to produce some form of work (see Figure 2-2) Work, in this case, occurs when energy goes through a transformation or change Heat, light, chemical action, sound, and mechanical motion are some of the common forms of work produced by a load device As a general rule, a very large portion of all energy produced by the source is consumed by the load de-vice during its operation The load is typically the most prominent part of the entire system because of its obvious work function

The indicator of a system is primarily designed to display certain

op-erating conditions at various points throughout the system In some tems the indicator is an optional part, while in others it is an essential part

sys-in the operation of the system In the latter case, system operations and adjustments are usually critical and are dependent upon specific indica-tor readings The term “operational indicator” is used to describe this ap-plication Test indicators are also needed to determine different operating values In this role, the indicator is only temporarily attached to the sys-

Electrical

Figure 2-2 Distribution path for electrical power from

its source to where it is used (Courtesy Kentucky Utilities Co.)

Power System Fundamentals 21

tem, in order to make measurements Test lights, meters, oscilloscopes, chart recorders, and digital display instruments are some of the common indicators used in this capacity

A SIMPLE ELECTRICAL SYSTEM EXAMPLE

A flashlight is a device designed to serve as a light source in an gency, or as a portable light source In a strict sense, flashlights can be clas-

emer-sified as portable electrical systems They contain the four essential parts

needed to make this classification Figure 2-3 is a cutaway drawing of a flashlight, with each component part shown in association with its appro-priate system block

The battery of a flashlight serves as the primary energy source of the

system The chemical energy of the battery must be changed into cal energy before the system becomes operational The flashlight is a syn-thesized system because it utilizes two distinct forms of energy in its op-eration The energy source of a flashlight is a expendable item It must be replaced periodically when it loses its ability to produce electrical energy.The transmission path of a flashlight is commonly through a metal casing or a conductor strip Copper, brass, and plated steel are frequently used to achieve the transmission function

electri-The control of electrical energy in a flashlight is achieved by a slide switch or a push-button switch This type of control simply interrupts the transmission path between the source and the load device Flashlights are primarily designed to have full control capabilities This type of control is achieved manually by the person operating the system

Figure 2-3 Cutaway drawing of a flashlight

The load of a flashlight is a small incandescent lamp When cal energy from the source is forced to pass through the filament of the lamp, the lamp produces a bright glow Electrical energy is first changed into heat energy and then into light energy A certain amount of the work

electri-is achieved by the lamp when thelectri-is energy change takes place

The energy transformation process of a flashlight is irreversible It starts at the battery when chemical energy is changed into electrical ener-

gy Electrical energy is then changed into heat energy and eventually into light energy by the load device This flow of energy is in a single direction When light is eventually produced, it consumes a large portion of the elec-trical energy coming from the source When this energy is exhausted, the system becomes inoperative The battery cells of a flashlight require peri-odic replacement in order to maintain a satisfactory operating condition.Flashlights do not ordinarily employ a specific indicator as part of the system Operation is indicated when the lamp produces light In a strict sense, we could say that the load of this system also serves as an indicator In some electrical systems the indicator is an optional system part

ENERGY, WORK, AND POWER

An understanding of the terms “energy,” “work,” and “power” is necessary in the study of electrical power systems The first term, “en-ergy,” means the capacity to do work For example, the capacity to light a light bulb, to heat a home, or to move something requires energy Energy exists in may forms, such as electrical, mechanical, chemical, and heat If energy exists because of the movement of some item, such as a ball roll-ing down a hill, it is called kinetic energy If energy exists because of the position of something, such as a ball that is at the top of the hill but not yet rolling, it is called potential energy Energy is one of the most important factors in our society

A second important term is “work.” Work is the transferring or forming of energy Work is done when a force is exerted to move some-thing over a distance against opposition, such as when a chair is moved from one side of a room to the other An electrical motor used to drive a machine performs work Work is performed when motion is accomplished against the action of a force that tends to oppose the motion Work is also done each time energy changes from one form into another

trans-Power System Fundamentals 23

Sample Problem: Work

Work is done whenever a force (F) is moved a distance (d), or:

W = F × d, where

W = work in joules

F = force in newtons

d = distance the force moves in meters

Given: An object with a mass of 22Kg is moved 55 meters

Find: The amount of work done when the object is moved

Solution: The force of gravity acting on the object is equal to 9.8 (a constant that applies to objects on earth) multiplied by the mass of the ob-ject, or:

F = 9.8 × 22 Kg = 215.6 newtons

W = F × d

= 215.6 × 55

W = 11,858 joules

A third important term is "power." Power is the rate at which work is

done It concerns not only the work that is performed but the amount of

time in which the work is done For instance, electrical power is the rate at

which work is done as electrical current flows through a wire Mechanical power is the rate at which work is done as an object is moved against op-position over a certain distance Power is either the rate of production of energy or the rate of use of energy The watt is the unit of measurement of power

Sample Problem: Power

Power is the time rate of doing work, which is expressed as:

W

P = ——, where

t

P = power in watts

W = work done in joules

t = time taken to do the work in seconds

Given: An electric motor is used to move an object along a

convey-or line The object has a mass of 150 kg and is moved 28 meters in 8 onds.

sec-Find: The power developed by the motor in watts and horsepower units

Solution:

Force (F) = 9.8 × mass

= 9.8 × 150 kg

F = 1470 newtonsWork (W) =F × d

=1470 × 28 m

W = 41,160 joulesPower (P) = W/t

= 41,160/8

P = 5,145 watts

PHorsepower = ——, since

746

1 horsepower = 746 W

hp = 5,145/746 = 6.9 hp

The Electrical Power System

A block diagram of the electrical power systems model used in this

textbook is shown in Figure 2-4 Beginning on the left, the first block is Electrical Power Measurement Power measurement is critical to the effi-cient operation of electrical power systems Measurement fundamentals and power measurement equipment are discussed in Unit I of this text-book The second block is Electrical Power Production Unit II presents the electrical power production systems used in our country Once elec-trical power has been produced, it must be distributed to the location where it is used Electrical Power Distribution Systems are discussed in Unit III Power distribution systems transfer electrical power from one location to another Electrical Power Conversion Systems (Unit IV), also

Power System Fundamentals 25

called electrical loads, convert electrical power into some other form, such as light, heat, or mechanical energy Thus, power conversion sys-tems are an extremely important part of the electrical power system The last block, Electrical Power Control (Unit V), is probably the most com-plex of all the parts of the electrical power system There are almost un-limited types of devices, circuits, and equipment used to control electri-cal power systems

Figure 2-4 Electrical Power Systems Model

Each of the blocks shown in Figure 2-4 represents one important part

of the electrical power system Thus, we should be concerned with each one as part of the electrical power system, rather than in isolation In this way, we can develop a more complete understanding of how electrical power systems operate This type of understanding is needed to help us solve problems that are related to electrical power We cannot consider only the production aspect of electrical power systems We must under-stand and consider all parts of the system

TYPES OF ELECTRICAL CIRCUITS

There are several basic fundamentals of electrical power systems Therefore, the basics must be understood before attempting an in-depth study of electrical power systems The types of electrical circuits associ-ated with electrical power production or power conversion systems are (1) resistive, (2) inductive, and (3) capacitive Most systems have some combination of each of these three circuit types These circuit elements are also called loads A load is a part of a circuit that converts one type of energy into another type A resistive load converts electrical energy into heat energy

In our discussions of electrical circuits, we will primarily consider alternating current (AC) systems at this time, as the vast majority of the electrical power that is produced is alternating current Direct current (DC) systems will be discussed in greater detail in Chapter 7

POWER IN DC ELECTRICAL CIRCUITS

In terms of voltage and current, power (P) in watts (W) is equal to voltage (in volts) multiplied by current (in amperes) The formula is P = V

× I For example, a 120-V electrical outlet with 4 A of current flowing from

it has a power value of

P = V × I = 120 V × 4 A = 480 W

The unit of electrical power is the watt In the example, 480 W of power are converted by the load portion of the circuit Another way to find power is:

V2

P = ——

RThis formula is used when voltage and resistance are known, but current is not known The formula P = F × R is used when current and resistance are known DC circuit formulas are summarized in Figure 2-5 The quantity in the center of the circle may be found by any of the three formulas along the outer part of the circle in the same part of the circle This circle is handy to use for making electrical calculations for voltage, current, resistance, or power in DC circuits

It is easy to find the amount of power converted by each of the tors in a series circuit, such as the one shown in Figure 2-6 In the circuit shown, the amount of power converted by each of the resistors, and the total power, are found as follows:

resis-1 Power converted by resistor R1:

Power System Fundamentals 27

When working with electrical circuits, you can check your results by using other formulas

Power in parallel circuits is found in the same way as power in series circuits In the example shown in Figure 2-7, the power converted by each

of the resistors, and the total power of the parallel circuit, are found as lows:

fol-1 Power converted by resistor R1:

V2 302 900

P1 = — = —— = —— = 180 W

R1 5 5

Figure 2-5 Formulas for finding voltage, current, resistance, or power

Figure 2-6 Finding power values in a series circuit

2 Power converted by resistor R2:

Figure 2-7 Finding power values in a parallel circuit.

The watt is the basic unit of electrical power To determine an

actu-al quantity of electricactu-al energy, one must use a factor that indicates how long a given power value continued Such a unit of electrical energy is called a watt-second It is the product of watts (W) and time (in seconds) The watt-second is a very small quantity of energy It is more common to measure electrical energy in kilowatt-hours (kWh) It is the kWh quan-tity of electrical energy that is used to determine the amount of electrical utility bills A kilowatt-hour is 1000 W in 1 h of time, or 3,600,000 W per second

As an example, if an electrical heater operates on 120 V, and has a resistance of 200, what is the cost to use the heater for 200 h at a cost of 5 cents per kWh?

P = — = —— = ——— = 720 W = 0.72 kW

Power System Fundamentals 29

2 There are 1000 W in a kilowatt (1000 W = 1 kW)

3 Multiply the kW that the heater has used by the hours of use:

MAXIMUM POWER TRANSFER

An important consideration in relation to electrical circuits is mum power transfer Maximum power is transferred from a voltage source

maxi-to a load when the load resistance (RL) is equal maxi-to the internal resistance

of the source (RS) The source resistance limits the amount of power that can be applied to a load Electrical sources and loads may be considered

as diagrammed in Figure 2-8

For example, as a flashlight battery gets older, its internal resistance increases This increase in the internal resistance causes the battery to supply less power to the lamp load Thus, the light output of the flash-light is reduced

Figure 2-9 shows an example that illustrates maximum power transfer The source is a 100 V battery with an internal resistance of 5

Ω The values of IL, Vout, and power output (Pout) are calculated as lows: